Icatibant

Hereditary angioedema attacks are driven by uncontrolled bradykinin generation, which binds endothelial B2 receptors and opens intercellular junctions, letting plasma leak into subcutaneous and submucosal tissue. Icatibant is a decapeptide analogue of bradykinin containing five non-natural amino acids, which makes it resistant to the peptidases that clear the natural ligand while retaining high B2 receptor affinity. It occupies the receptor competitively without activating it, so the swelling stops progressing and begins to resolve. Because it acts downstream at the receptor, it works regardless of whether the underlying defect is C1 inhibitor deficiency, dysfunction, or an ACE-inhibitor-induced bradykinin excess.

Targets: Bradykinin B2 receptor

• · 30 mg (3 mL of 10 mg/mL) subcutaneously. If the response is inadequate or symptoms recur, repeat after 6 hours, to a maximum of 3 doses (90 mg) in 24 hours. Laryngeal attacks still require emergency department observation after self-injection.

Work out your exact syringe units →

• very commonInjection-site reaction - erythema, swelling, burning, itching— Occurs in almost every patient and typically settles within hours.
• commonDizziness
• commonHeadache
• commonNausea
• uncommonElevated transaminases

• Known hypersensitivity to icatibant.
• Reliance on icatibant alone for a laryngeal attack without seeking emergency care - airway attacks can outpace the drug.
• Ischaemic heart disease or recent stroke warrant caution, since B2 blockade could theoretically worsen ischaemia by reducing bradykinin-mediated protective vasodilatation.

• conflictACE inhibitors — ACE inhibitors raise bradykinin and are a known cause of angioedema; they work directly against icatibant's purpose and should generally be stopped in HAE patients.
• redundantC1 esterase inhibitor concentrate — Both abort an acute attack through the same pathway at different points; one or the other is used, not both routinely.
• cautionlanadelumab — Lanadelumab is prophylactic and icatibant is on-demand, so they coexist, but breakthrough attacks on prophylaxis should prompt a review of the prophylactic regimen.

• · Attack frequency, severity and time to resolution in a written or app-based diary.
• · Airway status during and after any laryngeal attack - self-injection does not replace emergency evaluation.
• · Liver enzymes if symptoms suggest hepatic irritation.

FDA- and EMA-approved prescription drug for acute hereditary angioedema in patients 18 and older, dispensed for patient self-administration.

• Firazyr (icatibant) FDA prescribing information (label)
• Cicardi et al. 2010, FAST-1 and FAST-2 icatibant trials in hereditary angioedema (trial)
• Lumry et al. 2011, FAST-3 randomised trial of icatibant (trial)

Hereditary angioedema is a bradykinin disease, not a histamine disease, and that single fact explains why antihistamines, steroids and adrenaline do nothing for it. C1-esterase inhibitor normally restrains factor XIIa and plasma kallikrein; when it is deficient or dysfunctional, kallikrein runs unchecked, cleaves high-molecular-weight kininogen and floods the tissue with bradykinin. Bradykinin acting on the constitutively expressed B2 receptor on vascular endothelium triggers Gq signalling, raises intracellular calcium, activates eNOS and phospholipase A2, and disassembles VE-cadherin junctions, so plasma leaks into the interstitium. That is the swelling. Icatibant is a competitive B2 antagonist with affinity comparable to bradykinin itself, so it occupies the receptor and the leak stops even though the bradykinin is still being made. Two consequences follow from that mechanism. First, it treats the attack rather than the disease: kallikrein is still active, bradykinin is still being generated, and when icatibant clears with its 1.4-hour half-life the attack can resume, which is why up to three doses in 24 hours are permitted. Second, it works in bradykinin-mediated angioedema of other causes, which is the basis for its off-label use in ACE inhibitor-induced angioedema, although the randomised evidence there is mixed. The five non-natural residues are not decoration; they are what let a peptide antagonist survive subcutaneous injection with 97 percent bioavailability and be self-administered from a prefilled syringe by a frightened patient.

Injection site reactions happen in almost everyone, with erythema, swelling, burning and itching at the site within minutes; this is expected and is not an allergic reaction. The real failure mode is delay: icatibant works dramatically better the earlier in an attack it is given, and a patient who waits to see whether the swelling is going to be bad loses hours of the benefit. Laryngeal attacks are the other one: icatibant is the right drug, but a laryngeal attack still requires being somewhere an airway can be secured, and self-injection at home is not a substitute for that. About one attack in ten needs a second dose, and up to three doses in 24 hours are permitted at six-hour intervals. Finally, patients are frequently given icatibant for histaminergic angioedema after a misdiagnosis, where it will do nothing.

• Bradykinin B2 receptor — Label states affinity similar to bradykinin itself; competitive antagonism

  Blocks bradykinin-driven endothelial junction disassembly and plasma extravasation, terminating the angioedema attack. Demonstrated in humans by abolition of bradykinin-induced forearm vasodilation.

• Bradykinin B1 receptor

  Not meaningfully antagonised. B1 is inducible and upregulated in inflammation, which is one proposed reason for incomplete responses in some attacks.

• FAST-1 Phase 3 · n=56 · 2010

  Median time to clinically significant symptom relief after a single 30 mg subcutaneous dose versus placebo: 2.5 hours versus 4.6 hours (p=0.14, not significant on the original endpoint). The FAST-1 endpoint definition was widely criticised and revised for FAST-3.

• FAST-2 Phase 3 · n=74 · 2010

  Median time to clinically significant symptom relief versus oral tranexamic acid 3 g daily: 2.0 hours versus 12.0 hours (p<0.001).

• FAST-3 Phase 3 · n=88 · 2011

  Median time to 50 percent or greater reduction in symptom severity for cutaneous or abdominal attacks: 2.0 hours with icatibant versus 19.8 hours with placebo (p<0.001). Onset of primary symptom relief 1.5 versus 18.5 hours. This is the trial that settled the question.

Time to first symptom improvement is under an hour in most patients, with median time to 50 percent symptom reduction of about 2 hours and near-complete relief around 8 hours. Peak plasma concentration is at 45 minutes and the drug is essentially gone by six to eight hours, which is exactly the redosing interval.

Icatibant is on-demand rescue and sits underneath, not instead of, long-term prophylaxis. Combining it with C1-inhibitor concentrate is mechanistically redundant but not dangerous and is done when a severe attack is not responding. The interaction worth knowing is with ACE inhibitors: ACE is the main enzyme degrading bradykinin, so an ACE inhibitor raises bradykinin and is essentially contraindicated in HAE. Ecallantide works one step upstream at kallikrein and is an alternative rather than a partner. Antihistamines, steroids and adrenaline are not partners, they are placebo in this disease, and the specific harm is the time wasted giving them.

Against ecallantide: icatibant blocks the receptor, ecallantide blocks kallikrein one step upstream. Icatibant can be self-administered because it has no meaningful anaphylaxis risk; ecallantide carries a boxed anaphylaxis warning and must be given by a clinician. That single difference is why icatibant won the on-demand market. Against C1-inhibitor concentrate: C1-INH replaces the missing protein and works further upstream, is usable in pregnancy and in children where icatibant data are thinner, but needs intravenous administration. Against the prophylactic agents lanadelumab and berotralstat: different job entirely; those prevent attacks, icatibant stops one that has started.

Priced per 30 mg syringe rather than per month, and the number depends entirely on attack frequency. Brand Firazyr was one of the more expensive per-dose rescue drugs in medicine; multiple generics including Sajazir have since entered the US market and cut that substantially. I did not verify current pricing.

• ?Plasma protein binding is not given in the label and I did not resolve a primary figure.
• ?The label describes B2 affinity qualitatively as similar to bradykinin rather than giving a Ki; published Ki values in the low nanomolar range exist but I did not verify a specific number here.
• ?Efficacy in ACE inhibitor-induced angioedema is genuinely contested, with a positive European trial and a negative larger multicentre trial, and I did not resolve that literature in this session.

• Icatibant, a new bradykinin-receptor antagonist, in hereditary angioedema Cicardi M, Banerji A, Bracho F, et al., N Engl J Med, 2010 · PMID 20818888

  FAST-1 and FAST-2 reported together. Note that FAST-1 missed its primary endpoint.

• Randomized placebo-controlled trial of the bradykinin B2 receptor antagonist icatibant for the treatment of acute attacks of hereditary angioedema: the FAST-3 trial Lumry WR, Li HH, Levy RJ, et al., Ann Allergy Asthma Immunol, 2011 · PMID 22123383

  The definitive placebo-controlled result, with the revised endpoint.

• Pharmacokinetics of single and repeat doses of icatibant Leach JK, Spencer K, Mascelli M, McCauley TG, Clin Pharmacol Drug Dev, 2015 · PMID 27128215

  Source of the dose-proportionality and no-accumulation findings for three 30 mg doses at 6-hour intervals.

• Inhibition of bradykinin-induced vasodilation in human forearm vasculature by icatibant, a potent B2-receptor antagonist Cockcroft JR, Chowienczyk PJ, Brett SE, Ritter JM, Br J Clin Pharmacol, 1994 · PMID 7833220

  Direct human proof of target engagement, seventeen years before approval.

• Icatibant for multiple hereditary angioedema attacks across the controlled and open-label extension phases of FAST-3 Lumry WR, Farkas H, Moldovan D, et al., Int Arch Allergy Immunol, 2015 · PMID 26556097

  Durability across repeated attacks; no tachyphylaxis over many treated attacks.